1. Field of the Invention
The present invention relates generally to a self-adaptive Multiple-Input Multiple-Output (MIMO) technology using a channel fading correlation matrix, and more particularly to a self-adaptive MIMO transmission/reception system and method using an antenna set, a constellation size and transmission power in a MIMO transmission/reception system.
2. Description of the Related Art
MIMO technology is implemented to effectively improve fading channel capacity. Since a transmitter and receiver are provided with multiple antennas, respectively, MIMO technology is considered as an extension of dual-antenna diversity. However, MIMO technology effectively uses a code reuse technology and modulates a plurality of different data streams using the same channel and scrambling codes. This MIMO system controls channel fading using multiple antennas. Channel capacity linearly increases according to the number of antennas. In other words, radio channel capacity may be improved twice or more using MIMO channels and spectral efficiency may be improved twice or more without increasing bandwidth and antenna transmission power. To effectively separate sub data streams of the same spread spectrum code, a large interval between antennas is maintained, thereby preventing mutual interference between signals.
When MIMO technology is used, both channel capacity and channel reliability can be improved, and a bit error rate can be reduced. That is, the channel capacity can be improved using spatial reuse provided by MIMO channels, the reliability can be improved and the bit error rate can be reduced using spatial diversity provided by MIMO channels. To implement spatial reuse gain, a Bell Labs Layered Space Time (BLAST) algorithm, a Zero Forcing (ZF) algorithm and a Minimum Mean Square Error (MMSE) algorithm are mainly used. The BLAST algorithm has superior performance and low complexity, and uses the ZF algorithm and applies an interference cancellation technology to the ZF algorithm.
Diagonal-BLAST (D-BLAST) is a space-time technology and provides a system in which capacity linearly increases according to an increase of n when bandwidth and transmission power are fixed. This may improve spectral efficiency and may be widely applied in the future. When the number of receive antennas increases, the D-BLAST technology may reduce interference between channels, but computation may be complex.
To improve the performance of the BLAST system, a preceding technology has been adopted. However, the technology should feed back all correlation matrices to a transmitter. Antenna selection and antenna power and code rate control are performed. A conventional self-adaptive MIMO transmission/reception method maximizes the margin of a minimum Signal to Noise Ratio (SNR) by selecting an antenna set and a constellation mapping scheme. A system designed as described above uses the same constellation between transmit antennas and neglects a difference between the transmit antennas. When transmission power is considered, there are drawbacks in that the same power used for the transmit antennas may not be cost-effective and a full search should be performed for the antenna set.
When a data rate and a ZF receiver are fixed, a small number of transmit antennas may achieve high diversity order. However, a constellation size is large and a distance between constellations is small. A large number of transmit antennas may achieve low diversity order. However, a constellation size is small and a distance between constellations is large.
A Distributed Wireless Communication System (DWCS) should select a virtual cell for an arbitrary user. If the virtual cell for the user is formed in a state in which a large number of distributed antennas in uplink are selected, complexity and interference simultaneously increase. It is more important to set a virtual cell in downlink as compared with uplink. When a service is provided to an arbitrary user by selecting multiple antennas, low-quality antennas consume a relatively large amount of power. When a small number of antennas are selected, the degree of freedom of a channel is low, and therefore, high throughput is not implemented.